1. Field of the Invention
The present invention relates to winding lengths of material on a package.
2. Description of the Prior Art
Precision wound packages of lengths of materials, such as textile yarns, are well known in the art and have been used as the industry standard because of their uniform over-end take-off tension during removal of the length of material and due to their attractive high quality appearance which is unique to precision wound packages. Precision wound packages are so named because the length of material is traversed in a precise pattern across the package as the package rotates and winds the length of material thereon. This pattern avoids one wrap of the length of material from being overlaid on an adjacent wrap of the length of material in a given helical band of the package P. Such overlay, which is common in cross-wound (non-precision wound) packages, produces poor material take-off tension uniformity and can also cause "bumps" which result in vibration during rotation of the package.
Lengths of material that need to be wound at a constant or nearly constant speed are precision wound at low material speeds because of the inherently higher helix angle utilized at the beginning of winding the package than at the end. As used herein "helix angle" is the angle between a lengthwise axis of the length of material being supplied to the package and a plane perpendicular to a lengthwise axis of the package. At a constant, or nearly constant yarn speed the higher helix angle at the beginning of winding the package requires the length of material M to be traversed at a higher traverse frequency at the beginning of winding the package than the traverse frequency at the end of winding the package P. At high winding speeds however, the required traverse frequency may be mechanically unattainable at the beginning of winding the package or may result in an unacceptably low helix angle at the end of winding the package.
U.S. Pat. No. 4,049,211 to Spescha discloses a winding apparatus wherein the actual winding ratio step decreases with increasing diameter of the package, e.g., see FIG. 3 of the Spescha patent. The Spescha patent, however, discloses that each step in actual winding ratio is at least two integer steps. Moreover, the Spescha patent discloses that a ratio of actual winding ratio to integer winding ratio closest adjacent the actual winding ratio during winding, hereinafter "integer offset ratio", varies for the different values of actual winding ratio utilized during winding of the package. It is believed that utilizing different integer offset ratios during winding produces differences in spacing between centers of adjacent wraps of the length of material wound at different actual winding ratios.
It is therefore an object of the present invention to overcome these problems and others by providing a method and apparatus for winding packages with the appearance and take-off performance of precision wound packages while avoiding unacceptably high or low traverse speeds at the beginning and end of the package, respectively. It is an object of the present invention to provide a method and apparatus for winding a package, wherein the actual winding ratio is step decreased during the winding of the package and the integer offset ratio is constant throughout the winding of the package. It is an object of the present invention to provide a method and apparatus for winding a package wherein the actual winding ratio step decreases during the winding of the package between adjacent an integer winding ratio and adjacent a sub-integer winding ratio in a manner whereby a ratio of the actual winding ratio to sub-integer winding ratio closely adjacent the actual winding ratio, hereinafter "sub-integer offset ratio" is constant during winding of the package and the integer winding ratio is constant throughout winding of the package.